Apparatus for measuring or indicating roughness or undulations of a surface



Oct- 4, 194 R E. REASON ET AL APPARATUS FOR MEASURING OR INDICATINGROUGHNESS OR UNDULATIONS OF A SURFACE Filed June 12, 1944 llSheets-Sheet l y W% Attorney Oct. 4, 1949.

R. E. REASON ET AL 3,66 APPARATUS FOR MEASURING OR INDICATING ROUGHNESSOR UNDULATIONS OF A SURFACE Filed June 12', 1944 ll Sheets-Sheet 2 Atiorne y Oct. 4, 1949. R. E. REASON ET AL 2,483,658

APPARATUS FOR MEASURING OR INDICATING ROUGHNESS OR UNDULATIONS OF ASURFACE Filed.June 12, 1944 3 ll Sheets-Sheet 3 I 2 f I 4 ui. E 1 j!- I1 i V W H j H 2 in lnve ntor Rmunno ju'muzvo F5050 Attorney Oct. 4,1949. R. E. REASON ET AL 2,483,663

APPARATUS FOR MEASURING OR INDICATING RQUGHNESS QR UNDULATIONS OF ASURFACE Filed June 12, 1944 11 Sheets-Sheet 4 uentor EJSDN I mean RD [0Mduo fr Attorney Oct. 4, 1949. R. E. REASON ET AL 2,483,568

APPARATUS FOR MEASURING OR INDICATING" ROUGHNESS OR UNDULATIONS OF ASURFACE Filed June 12, 1944 ll Sheets-Sheet 5 N3 0 Q6 0 [a o R/ o s Q5 iQ/ 0 F I a 7 D N /v 4 \o i R O J J a 1 TI .1

m g 5 j F r RJCHRRD EDMUNO Ajnventur Attorney APPARATUS FOR MEASURING ORINDICATING -Oct. 4, 1949. Q R. E. REASON ET Ax; 2,483,668

ROUGHNESS OR UNDULATIONS OF A SURFACE Filed June 12, 1944 llSheets-Sheet 6 I I ca3c Inventor 'R/CHHRO EDMUND ERJM/ Attorney Get. 4,1949.

Filed June 12, 1944 ll Sheets-Sheet F/GZ O v f 05 e $2 u- A c InventorRENE; [om 0N0 /i Eas v A ttorne y Oct. 4, 1949. R. E. REASON ET AL2,483,568

APPARATUS FOR MEASURING OR INDICATING ROUGHNESS OR UNDULATIONS OF ASURFACE 11 Sheets-Sheet 8 Filed June 12, 1944 P6 F/GS).

wow WW MMS m w w I"? m 0 K N M K V. m B J m g F V3 P s 7 s m m a 3 P E IH. G 1111.. F m o Oct. 4, 1949. R. E. REASON ET AL. 2,483,668

APPARATUS FOR MEASURING 0R INDICATING ROUG'HNESS OR UNDULATIONS OF ASURFACE Filed June 12. 1944 ll Sheets-Sheet 9 Inventor fi/(Aard 5 Reasonna/a I? Herr/dye 6/ any l Attorneys Oct. 4, 1949. REASON ET AL 2,483,668

APPARATUS FOR MEASURING OR INDICATING ROUGHNESS OR UNDULATIONS OFA'SURFACE Fil ed June 12, 1944 11 Shets-Shet 1o Inventor Klan ma Emu/v0RE/ia Attorney Oct. 4, 1949. R. E. REASON ET AL APPARATUS'FOR MEASURINGOR INDICATING ROUGHNESS OR UNDULATIONS OF A SURFACE ll Sheets-Sheet 11Filed June 12, 1944 FD W .t.

Patented Oct. 4, 1949 UNITED TATES APPARATUS FOR MEASURING OR INDICAT-ING ROUGHNESS R UNDULATIONS OF A SURFACE Richard Edmund Reason andDonald Roy Berridge, Leicester, England, assignors to Taylor, Taylor &Hobson Limited, Leicester, England, a company of Great BritainApplication June 12, 1944, Serial No. 539,862;

In Great BritainMarch Section 1, Public Law 690, August 8, 1946 Patentexpires March'24, 1968 This invention relates to apparatus for measuringorindicating the roughnesses or undulations of a surface, of the kind inwhich a stylus is traversed over the surface and the movements of thestylus normal or approximately normal to the surface during suchtraversing are trans formed into electrical energy for controlling ameasuring or' indicating instrument. The invention is especiallyconcerned with a pick-up unit for use in such apparatus.

The present applicants United States of America patent specification No.2,329,084 describes one such pick-up unit, comprising a casing orframework which can be located in any chosen position relatively to thesurface under investigation, a pick-up head carried thereby, and meansfor driving the pick-up head over the surface at any oneof two or moredifferent speeds, the pick-up head itself consisting of a skid engagingwith the surface over an appreciable area, a stylus projecting throughthe skid to the surface and movable relatively to the skid duringtraversing, and a differential electromagnetic detector deviceresponsive to suchrelative movement for controlling the measuring orindicating instrument. This arrangement enables the stylus to betraversed at will either at a relatively slow speed for operating a penrecorder or like instrument or at a relatively high speed for operatingan average meter to give a measure of the average roughness or wavinessof the surface.

In the preferred construction described in such prior specification thepick-up head is carried by a horizontal shaft movable longitudinally inbearings in the walls of the casing nearthe bottom thereof. This shaftcarries a bracket on the top of which is a half-nut engaging with ascrewthreaded driving shaft driven through changespeed gearing from anelectric motor, the teeth of the screwthread being asymmetrical afterthe manner of a ratchet to permit the half-nut to travel freely in thereverse directionand thereby facilitate resetting to the startingposition after a forward traverse has been completed.

The present invention has for its object to provide an improvedconstruction of pick-up unit wherein possible errors in the traversingmove ment due for example to friction at the bearings of the horizontalshaft are eliminated or minimised. A further objectof the invention isto enable the use of a skid on the pick-up head to be avoided.

The pick-up unit according to the invention comprises a casing'orframework which can be located in any chosen position relatively to the13 Claims. c1.73+105 surface under investigation, a pick-up headcarrying a stylus for engaging with the surface, a member carrying thepick-up head, link mechanism Within the casing comprising a group ofmutually pivoted links constituting in effect two straight-line linkagesrespectively constraining two points of the said member to perform atleast approximately straight-line movements in the same direction, anddriving means cooperating with the link mechanism to cause the memberand the pick-up headto be traversed over the surface along thestraight-line path determined by the link mechanism. With thisarrangement, the member will be constrained to make a bodilytranslational movement in which all parts of the member remain parallelto their original positions, so that the pick-up head may be mounted inany desired position on the member, without the necessity for the use ofa skid. The line joining the two constrained points of the member may becoincident with the direction of movement thereof or. may be at an anglethereto, and it is especially convenient to provide means whereby suchangle may be varied.

It should be made clear that the term straight line linkage is hereinused to mean agroup of mutually pivoted links so arranged as to bemainly or wholly contributory to the generation of a straight line or aclose approximation to a straight line by a point of the linkage suchpoint being known as the tracing point of the linkage. Thus the termincludes true linkages, wherein two or more points are fixed and thelinkage is otherwise unconstrained (except in some instances for stopslimiting the range of movement of the tracing point) and also guidedlinkages in which at least one point of the linkage is constrained to adefinite path by a fixed guide.

Amongst the true linkages may be mentioned various alternativeconstructions (including for example linkages of theWatt type) employingthree links, one of which carries the tracing point whilst the other twoare pivoted about fixed points and are also pivoted to the first link,the lengths of thethree links and thedistance between the fixed pivotsbeing appropriately interrelated.

The well-known example of a guided straightline linkage is theScott-Russell linkage compris ing two links, of which the first is twicethe length of the second which is pivoted about a fixed point and alsopivoted to the mid-point of the first link,' one end of the first linkconstituting the tracing point whilst the other end is constrained tomove along a straight guide collinear with the fixed pivot. Ihe accuracyof the straight line generated by the tracing point in the Scott-Russelllinkage depends'onjthe accuracy of the guide,

but a very close approximationtoa straight line Will he obtained in theportion of the trace close to the fixed pivot even with quite materialerrors Various Ways, but the accompanyingdrawingsillustrate a preferredconstruction of plcko-luplunitlaccasing A which houses the pen recorderor other device for giving the desired indication of thesurfacerqughness, Whilst the electrical parts of the apparatus arecarried in racks A on the f trolley.

' The vertical column B also carries a counterit eighth connected to thecasing C of the pick-up unit by acable passing over a pulley B at thetop of the column. -The casing C has a side plate C5 Qsee also, Figures2 to 7, especially Figures 2, fiandlliwhichcan slide up and down theface of the column B and has clamped to it at the sides ofthe columnbrackets C carrying rollers C cording to the invention, together withsome modi- I fications thereof, such preferred constru tio'rfias alsosome of themodifications) incorporating also the invention oftljecopend'ing application Serial No. 536,634; filed"May Z0, 194f1;;I1OW abandoned. "lnthes'edrawingsfi" Figure 1 is a general view fromtheside of one convenient arrangemento'fthe complete apparatusrjdi'iiieasurnig' surface roughness, incorporatingth e p u'pu'nit'according't'o the invention, FigiireZ 1s a horiiontal section on alargerscale of the pick jupunltthe'section'being taken on thebroli'nline IlT-TI ofFi'g iir B," Fl uiefis vertical sec on" on the lineIII- 111 ofFig'iirZ, Tag-ere ifis a side elevation of thepick-up unitwiththe cover plateof the'removd,

k 'res Sand 'eere tra sverse"v n l sections taken respectively on thelines {V V and VI- VI of la igure 3"l o'oking' towards the left in thatfigui': A

"Figure '7 is a transverse vertical section talcen bemtlp qin placeofthedouble scottffiussell V linkage used intlieconstructionfoiiFigure2%7;

Figures "l'cnl' lbl 14:0, if are diagrams similar to those of "Figuresll 113 but 's' ho'w i ng the'double'scott Rlussellflihlgagein t jieimiar' fdim aiiifllifi d i 5. 19 1 mi Fi llll l gib t ra h ii esl f a o heformj' actually"employedfinf the 1 construction .of Figures? to 7, and

Figuresd dto'19respectively show a plan View, a side elevation, a viewfrom below, a transverse 2 59 1 9 E l i 15, an an emeievatipnjviw d fromthe right of Figures" 15 w n, of an alternative practical ddristmgtion;,7 l "The surface-roughness measuring apparatus sho'vvn in'lfigure 1compr s s, a m'e supiort t the fori'n'jifa 'whe'eledtrol yAiip Ol/flgid, 't'h nieans indicated atAlfor'steadying the the 11051 Whn' h1?#91 5 3ar ie fwdrk apfg A2 o sitppe tin'e Kin, de red e i qzi i soil) e9 9Wiese enat sf 'e e e ed. may ipa fi fl mnlBi i the rent of a 1 generallyH {shaped girder,' on which bsf a' ng 'Lbiihe' hi -l fil ni i iusia l fe i x i sr v c r es area l The invention may be carried into practice ini "ii si' iresiiiieie it whichengage withthe inner faces of the flanges33 heco l umn B. Vertical movement of the cas g C on the column iscontrolled by a hand linoliD on the end of a shaft D passing throughtiaeasmgc, this shaft carrying a pinion D enggtgihg with a rack 13fitted to the column. The casing C can be locked in any chosen positionof adiustmenwe the when 1 y i s ns f. a we m t h areas a ba D4 wh h anslide i" i;, h s f a e i s ar D4 be n m ted l on itu in lly into r outof the locking position by meansy xa l qk sha D acwel e by. Mockl f d 'eD a at ent s. ande t D p. the oth erls'ide of the casing.

' The. pick-up head E is nquntgd on the end oi: a meme:eana s a' b 1EWhichpr ec freely through an opr ing n ear the b otto m of t id wa ecases Q a s movabl longi? ia l th e and themes-unmade b ng movabletogether relatively to casing for traversing the sylusEE.

T e ha n -sewed e s i ort d n -1 inecby n i m ehi -m h Qh sist v inessence of two iden ical scottglilussell linkages -ldis e e h l 'h liqii e aily Pa of c resp nd ng P9 9 h tw k a a rwhich. the bar ispivoted. to t e. inkage 'It. i

e, i mv ment ,at thi 0 describe the link: it i e a xam q Fit e 1 re ialii w arr ing t 0 complete Scott Ru s li ka s i hi -i m i el m an Fi ele i e 2 aws i dsho e i eme t l er e l ad n ei l sure. hi l tr tes. e

'ponf t tl t s' he trac n point whilst the ot r end a 'or b3 "carries aMilena? pr bi which enga e ilta li fl t aisht ea er r b T e w link or byis lpivo ted ethan end of th ice,

19 i qt ime-fi s .i ines -it o h an t a fixed comic or. 12 collinear With fi gu de ?"o fb tg i i-mei l tri' fil with t e st ht pa hei he uidedPoint a? or b? .or th fir ,be, 1 that each tracing point ei h ihi'e shha xe right angles tothe length. of, the

i l l y t, a or b gener ire? c ib? guide iii jofr til "The. qiit qu dmember e (which represents .the "traversing bar. E1 of Figures ,2 to? isrive d i th ii le inka e eat-he o; ae e in ieiefieed b? ande ii' m ew tion parallel to: the r line ii ning lthe two tracing points areseparated? by a. distance aqua to that between the two fixed pivotsalsct tthat etw en t e w l ix d 'u d iandb sq fihat the 'crngltrolledmember} ell no'v'e s are heal h;

Figure 14b shows a modification of this arrangement, in which anadditional link 11 connects the mid-points a and b of the two firstlinks, the length of the link d being equal to the'distance between thefixed pivots a and b". A single fixed guide 12 is employed for the twolinkages, the upper half of the first link a, rendered redundant by theadditional link (2, being omitted. 3

In the further development shown in Figure 140, the upper halves of thefirst links a, and b of both linkages are omitted, the additional link dbeing extended to pivot at the mid-point d of a control link d one end dof which engages through a roller with a fixed straight guide 01 whilstthe other end (1 is so-pivoted to the controlled member e that thecontrol link d always lies parallel to the first links a, and b of thetwo linkages. It will'be clear that, with this arrangement, the controllink d ensures that the additional link d always moves at exactly halfthe speed of the controlled member 6.

The accuracy of the straight-line path generated by the tracing point ofa Scott-Russell linkage will theoretically depend on the accuracy of thefixed straight guide, but in the portion of the path close to the fixedpivot, when the angle between the two links is very small, the degree ofaccuracy will be very high even if there are quite material errors inthe straightness of the guide. This being so, it will be clear that onlya negligibly small error will be introduced (in the portion of the pathclose to the fixed pivot) if the upper end of the first link isconstrained to move over a circular path of large radius approximatingto the usual fixed straight guide. Such a modification is shown inFigure 14d, wherein the end d of the control link d is pivoted to theend of a further link d of adequate length, lying approximately parallelto the direction of movement of the controlled member e and pivoted atits remote end to a fixed point d". It is convenient inpractioe toduplicate some of the links so as to enable the various elements to passone another without fouling and thus to permit the most accurate portionof the trace near the fixed pivot to be employed. It will thus be seenthat the link d and connecting parts in effect form a guide whichcontrols the angular relationship between the links I), 1) throughoutall angular positions of the link b about its pivotal point on thecasing.

Adjustment'of the'angle' between the direction of movement of the twotracing points andthe line joining them, can readily'be efiected byadjusting the position of the fixed pivotd". Theoretically, suchadjustment should take place about i the fixed pivot d but in practicethe error involved in efiecting the adjustment about a pivot d (seeFigure 14c) located in a convenient position between the pivots d and dis negligibly small. As

has been mentioned, it is the arrangement of Figure 14a, which isactually used in the preferred construction of Figures 2 to '7, thoughany of the other modifications just described could have been employed,if desired.

Thus in the preferred practical construction the complete link mechanismcomprises a horizontal base plate F, which is secured to the base of thecasing C and to which are clamped at the-four corners of a rectanglefour flat spring ligaments GGr HI-I each of which constitutes a fixedpivot for an upwardly projecting arm G or G or H or H the two front armsG and G thus pivotiing about a fixed axis constituted by one side of therectangle and together makin up th second link or one linkage, whilstthe two rear arms H n similarly pivot about a parallel fixed axisconstituted by the opposite side of the rectangle and together make upthe second link of the other linkage. Each of these four arms G G H Hcarries a ligament spring at its upper end, and the four ligamentsprings G G H H are clamped to a horizontal plate J (constituting theadditional link) at the four corners of a rectangle similar to that onthe base plate F.

Between the front pair of ligament hinges (3: 6? the horizontal plate Jcarries a downwardly projecting ligament spring K constituting a pivotfor another arm K of the same length as the four arm G G H H alreadymentioned, and an exactly similar arm L is provided between the rearpair of ligament hinges H I-I These two arms K 11 constitute the firstlinks of the two linkages, or more strictly the lower halves of thefirst links, the upper halves being omitted. At their lower ends thesetwo arms K L carry further ligament springs K L which are clamped to thecontrolled bar E the spacings between the front and rear ligament hingesbeing the same on the base F, onthe horizontal plate J and on thecontrolled bar E so that in their normal rest positions all the frontligament hinges GG G G KK lie in the same vertical plane, as also do allthe rear ligament hinges HH H I-I LL The base plate F and'the controlledchannel-shaped bar E are suitably recessed to provide clearance for themovement of the bar. Although separateligament hinges have been referredto at the top and bottom of each vertical arm, it will usually besatisfactory in practice to employ a continuous ligament for th twohinges, the main part of such ligament between the two pivots beingclamped between rigid plates to form thegarm itself.

' The fixed base plate F forms part of a shaped supporting frameworkwithin the main casing, this framework including recessed vertical sidewalls 'l and a slotted horizontal wall F extending between the sidewalls above the controlled channel-shaped bar E and below the horizontalplate J (as well as various brackets for supporting parts of the drivingmechanism to be described later), the controlled bar E thus movinglongitudinally within a skeleton rectangular tubular structure.

The horizontal plate J and the controlled bar E each extend back beyondthe rear linkage for the same distance and carry at their rear endshorizontal flat spring ligament hinges MM constituting respectively amid-point pivot and a bottom pivot for the vertical control link M whoseupper endcarries a further-horizontal ligament M constituting. a pivotbetween the control link and the guidin link M which extends forward ina generally horizontal direction above the horizontal plate J. The frontend of the guiding link M is pivoted by a ligament spring M to a blockN, the bottom of which J's-attached to an intermediate part of a furthergenerally horizontal link N pivoted on a ligament hinge N at it rearendto a fixed bracket F on the base framework. The front end of thisfurther link N normally remains fixed during operation of the mechanism,but can be vertically adjusted about its pivotN through a small ran e bymeans of a threaded adjusting rod N extending through the top wall ofthe casing C to an adjustable hand knob N a. leaf spring Nibeingaseeiecs 57 rov ded. to :keep; .the El n N iim7 en agement with theme-NThus byo erating thehead knob the, further link Ni'will.-move,.a-boutgits .fiXfidzpivot N2 .at its rear endand-wi -lithus cause.the. guid- .ing; linkM to move about thesamemvot. therey dj stin t pp r..enchcf. fihfixCOfltlOl link .M forwa rds or backwards; thrpugh mshortdistance. This will have-the effect, of: varyin h {direction of-movementof: the; two tracing-iPQints.

That this is so, will befilearyfrcma a'cnnsiclera.

.tion. of the equivalent. linkage. arrangcmentwemm ving. a s rai ht. guie. Th ore ically; such e a n ngem n the str h uideshmd .zbe angularlyad-justable about the basic-v .fixed i vo.twith which it iscollin ar,and in suchcaasc the direction of movement of the; tracing pelints wouldbe at right anglegto theglflide in allangular of the controlled bar Ethrough a smallangleor either side ofthe normal: direction;,WhichiscQ-incident with the direction of the len th piithe bar, is especiallyadvantageous in constituting a fine adjustment tor-enabling thedirection of traversing of the stylus E to be accurately! co.- ordinatedwith. the surface. under investigation.

"In practice, this, is conveniently achieved, after coarse adjustment,by bringing the link. mechanism.into itsnorrnal zero. position, whereinthe links all lie vertically, and. then, by apreliminary adjustmentbringing t eindicating element to.,a

convenient point on the scalewhenthe stylus is engaging the surface inthis. .l lQSi iQn; .for

example in the case of a. Pen recorderbyvbringing the pen somewherenear. theflmiddlehof the paper. "The stylus'E is then moved along tthesurface by operation of the .driyingmechanism to be described below, andif 1th.e..dir.ecti0nofwtraversing is not accuratelyparallel.tothesllrftlce, the pen will move off the. paper ater.a shorttraverse (owing to the highhmagnification emgp d usting n bisthen-qperated in the appropriate directionto tilt the control link Mthrough the small anelemmessarv .to bring the pen backontothe-paperinthe new position, so that the gener al..dirction... ofthe trace after such adjustment will'be approximately the same as thelengthofthe paperrecord.

The mechanism for driving. thecontroHed. bar E for traversing thestylus. may. vary, but the drawingsshow .by way of example oneconvenient practical arrangement Whaliebythe. bar. can, be driven in theforward; traversing. direction, atone or other of twospeeds-arelatively. slow speed for operation of,.say, a pen.recorderhanda-relae t-ively high speedier operation of. anintegratingmeter for giving a reading ofwthe .faverage o hne of he s rfac -and.can. .he.quic k1y resetto its starting position in .readinessrfor-afurther forward traverse.

In this arrangement the controlleibar, E1, .car-

:8 upper-errata: cradlei0 .ioichanne1: section, ;the rod-being;.-pressed. upwardlylzbyna spring 0 and be- ;ing held; againstrotation: by apin-E-E extending horizontally fr0mi.the :bl0ck1E into a.short. vertical slotrO tin aibracket ,Otcarried by thecradle Q..The:'siot=O ;-also.= acts asa-stop to limit the upward: movementv.oii. the Y cradlegunderithe action of the spring. ,0 These parts areshown on a larger scalein-iFiguresB to 10. This pin,.E t0- gethen-withanotherjshorter pin l? slightly spaced from-.itand. likewise .carriedbythe block E also servessasga guide fora pi-n. P dependin:downwardlythrough a .slot in. the .cradlevO from a halfrnutl :Pcarried; in. the Bradle, The vtwo halfnuts- P engage respectivelywithtwo screwthreaded Shafts. QQ mounted horizon-tally in bearingscarried; by; .a bracket-F on the fixed framework and-extending; paralleltoioneanother in thedirectionof traversing,

Each half-nut-P, frts freely in its cradle O and rests on a leaf spring0 in the base of the cradle .u-rging it upwardl -y 1 into engagementwith the screwthreaded shaft Q or Q. The half-nutextends for thefull-length of the cradle but only a small portien atone end is.threadedto engage withthe, shaft,.-whilst a smooth portion P, at itsother-end acts as an abutment resting against the threads.- on. the;shaft, the: middle; portion being cutawayclear of theshaft. ,This middleportion and..-the end abutment. piecevareslotted longitudinally. at P3along the-centre: line. to provide accommodation for ahorizontal. link Ppivoted at, P5. to the middle. ofthehalf-nut and. extend- .ingto. the.endthereof, where the link is pivoted at; P to. the cradle.- 0 The;latter pivot pin P passes freely through a hole in the half-nut P, andthe former pivotpin P likewise passes freely through ahole in. thecradle O ,.and thetwo pins in these. larger holes act as stopsto limitthe .movementofthehalfenut in the cradle. I

.lItQwilllhe. clearthat with this arrangement the hal'ienut is free-(to.move .vertically within the ,sma1lilimitsjdefined..lby thestops and cantilt slightly insuchvertical movement, owing to the provision. of thehorizontal. pivoted link P, but

its horizontlalldriving movement is transmitted withoutfree playthroughthe-link P to the. eradle' O and'thence through the vertical rod 0 tothe controlled'bar Ekof the linkage.

One-of the two shaftsfQpis operativefora-relatlvelyslowspeed traversesuitable for ,use with a pen 'recorder, and the other Q for. a higherspeed-traverse suitable for obtainingan average measurementand ahand-operated change-over device isprovidedtoseIect-which drive shall beoperative. Thetwo shafts QQ are driven respectivelyfrom two smallelectric motors "Q Q through suitable gearing Q -atthe appropriatespeeds; The change-over devicemay consist of awtransverse spindle Q--mounted above the two shafts. andicarryinga pair of camdiscs-.Q Q (orthelequiva-lent). actingrespectively on parts'ofthe two cradlesiOwhichcarry the half-nuts. Thus intone ..operative:positionof the-spindleQ one of the half-nuts Will be held down outof-engagementiwit-h-itsscrewthread; whilst in the second :operative: position of the spindlethe other halfnut will-be: held out ofengagement with its screw thread:The change-over spindle is operated by .a hand. knob Q projecting; from.the side of the casing. C. The spindle. is also-uti1iseds to operatecontacts. Q controlling thezmotor. circuits so that the-appropriatemotor Q? or Q is. energisedv when .the corresponding half-nut isinrengagementzwith itsshaftQor. QL.

The two screwthreaded shafts are each pro- 9 vided with asymmetricalteeth, after the manner of a ratchet, so that the half-nuts P can slidefreely over the threads in one direction to facilitate quick resettingto the starting position, the traversing drive being eifective in eachcase in the forward direction only. This arrangement also has theadvantage that, should anything act to interfere with the movement ofthe controlled channel-shaped bar E during the traversing drive, thethread will ratchet idly without damage to the parts.

To effect starting and resetting a lever R is provided which is carriedby a hollow transverse spindle R which surrounds the spindle Q andprojects through the wall of the casing C to an actuating hand lever RThis lever R near its lower end abuts against a stud E projectinglaterally from the controlled bar, so that movement of the startinglever R in one direction from its normal position will push thecontrolled bar E back to the starting position ready for a new traverse.The starting lever B (in conjunction with the stud E on the controlledbar) also operates contacts in the motor circuits, the arrangement beingsuch that the appropriate motor starts up to effect the traverse whenthe starting lever is moved back to its normal position after resettingthe controlled bar.

For this purpose the starting contacts conveniently consist of an upperspring blade contact R and a lower spring blade contact R the startinglever R being so shaped that, when in its resetting position, itdepresses both spring blades and holds the contacts open. The stud E onthe controlled bar also engages with the upper spring blade R but doesnot effect the lower spring blade R Thus in the resetting position, thestarting lever holds both blades R and R depressed, with the contactsopen. When the starting lever is moved back to its normal position,leaving the controlled bar E and its stud E in the resetting position,it releases both contacts by moving off their ends, but only the lowerblade R moves, since the upper blade remains depressed by the stud. Thecontacts therefore close when the starting lever gets back to the normalposition, and complete the circuit to the appropriate motor, asdetermined by the position of the clutch spindle Q The motor thereforestarts up and effects the traverse, during which the stud E moves alongthe upper spring blade R and finally comes off the end thereof, after apredetermined length of traverse, to release the upper blade and therebyopen the contacts and stop the motor. In the resetting movement thestarting lever R depresses the two blades R R simultaneously so that thecontacts remain open throughout the resetting movement and do not closeuntil the starting lever has returned to its normal position.

The controlled bar E also serves to operate further contacts associatedwith the circuit of the integrating meter used for the averagemeasurement, in order to ensure that such meter only comes intooperation after an initial short portion of the traversing movementsuflicient to ensure that the motor Q has reached its full speed andlikewise goes out of operation before the final portion of thetraversing movement during which the motor is coming to rest beforestopping. These contacts consist of three vertical spring blades R R R'clamped at their upper ends and extending down behind the rear end ofthe horizontal plate J. The two outer spring blades B B are electricallyconnected together and both, oo-

10 operate with the middle blade R which extends further down betweenjaws E carried by the controlled bar E In the resetting position at thebeginning of a traverse, the middle blade R is moved by the jaws E onthe controlled bar E into engagement with the front spring blade R andthe contacts are therefore closed. After the appropriate short initialportion of the traverse the middle blade R is moved out of engagementwith the front blade R, and thus opens the contacts. The contacts remainopen until shortly before the end of the traverse when the middle bladeR is brought into engagement with the rear blade R to close thecontacts.

The arrangement of the electromagnetic device in the pick-up headcontrolled by the movements of the stylus approximately normal to thesurface and of the measuring apparatus controlled thereby, forms no partof the present invention, but may be for instance as described in theUnited States of America patent specification application Serial No.378,836, filed Febru ary 13, 1941, now Patent No. 2,344,217 in the nameof the present applicant and another. I

The foregoing arrangement may be modified in various ways, for exampleby employing other forms of double straight-line linkage. Thus onealternative form of double linkage which may be used consists of twoidentical linkages of the Watt type, as shown diagrammatically in Figure11,

so disposed that lines joining corresponding points of the two linkagesall lie parallel to the line joining the two tracing points, at whichthe controlled bar is pivoted to the linkages. In each linkage, thetracing point lies at the mid-point S of .a normally horizontal link S.(the drawing showing the parts moved away from their normal centralpositions), The front end S of this-link S is pivoted to the lower endof a normally vertical link S and its rear end S is pivoted to the upperend of a normally vertical link S The two vertical links S 3 which areof equal lengths, are pivoted at their other ends to fixed points S 3respectively. The controlled bar S is pivoted to the linkages at the twotracing points S, and the spacing between these two pivots is equal tothe spacings between the two upper fixed pivots S and also to thatbetween the two lower pivots S'. It is not essential that the twovertical links. in each linkage should be of equal length, but if theyare unequal the tracing point should divide the horizontal link in thesame ratio as that between the vertical links and should be nearer tothe longer link. The Watt linkage gives only an approximation to astraight line, but the error from the true straight line is very smallwithin a moderate range of movement of the tracing point from the normalcentral position.

Another alternative form of double linkage is a double inverted Wattlinkage, as shown diagrammatically in Figure 12, again with the linesjoining corresponding points of the two inverted Watt linkages all,lying parallel to the line join- Such alternative double linkages may bemodifled by providing additional links parallel to the mentsto movepastone another .without fouling:

It is also'convenient in. practice:

and fiat spring ligaments are preferably employed: r

for the pivots.

Adjustment of the angle between thedirection ofmovement of the twotracing points and the line.

joiningthem can readily be effected by deforming: the"v parallelogramformed by the four .normally fixed pivots, and Figure-l3 shows amodification of- Figure 11 permittingsuch adjustment. In thismodification the two pairs of normally fixed pivots S S and S 8are-mounted respectively on twoade ditional lines T and T lying parallelto the-controlled :bar and interconnected by a pair of normally fixedparallel control links T 11 so as to'be constrained to remain parallelto one another.

Thedesired angular adjustment can be effected by somounting the normallyfixed control links:

'I T that they can'be rocked through anvappropriate angle aboutfixedpivots T T at corresponding=points of the links and can beclampedinx any; desired angular position.

Although it will usually be preferred toemploy ligament hinges forv thevarious pivots in the foregoingrarrangements, owing to theirfreedomfrom: I errors-due: to dirt'and frictional wear and'alsoto fshakein the joints, satisfactory results: can. be obtained "by means of balland socket i'joints; whereinnthe balls:.are pressed into engagement."

wlththe socketsbyclamping pressure exerted in. the direction of the.pivot axis, since such an arrangement is self-aligningand eliminates:errors due to shake.

Onesuch practical construction (employing a simplified form of thedouble Scott-Russell linkage used in the construction of Figures 2to7)is il-.

lustr-ated by way of example in Figures 15' to 19. Inthis constructionthe two links of the front linkage-are in theform of :platesevv disposedone behind: the other, the plate Vserving to con- 12" Atzits lower endthe link Xhas'recesses for two; balls "XlXZ, of which thefirst 'Xalsoiengages. in

a-recess ina portion of the base'W'whilst the 1 second X is mounted onthe-end of a short'dis- Itance' piece X whoseother end is also-formed asa ball X to engage in a recess in'a spring'strip' W clamped to the baseW. At its upper end the linkXihas on one side a recess for a ball Xengaging in'a recess in the body of the horizontal plate-W whilst on'theother side the link is provided With a horizontal groove to receive theflattened and of a hatchet-shaped distance piece X 'whose other end isformed as a ball X" engaging in a recess in a spring strip W clamped tothe horizontal plate W At its lower end the link Y has recessed fourloallsiz' Y of which the first Y engages in a recess in the controlledbar W and the second Y is formed on the end of a distance piece Y havingat its other end a ball Y engaging'in a recess in a spring strip Wclamped to the con-- trolledbar W At its niid-point the-link Y has onone side a recess for a ball Y engaging in a recess in the horizontalplate W and on the zsiiother side'a groove for receiving the flattenednect the fixed baseWwith the horizontal'plate W' i'whilst the otherplate V connects the horizontal'plate W 'with the controlled-barw lmountingof the plate V is shown in" detail in Figure 18.

Thus the plate V is conically or otherwise reballs V V -,thus providinga self aligning hinge- The lower balls V V "similarly engage in recessesin the body of the controlled free fromshake.

bar- W -and in a spring strip W clamped to such bar;

The-front plate V'also has recesses forfour' balls V V V V ofwhich theupper two V V engage in recesses in the body'of the horizontal plate Wand in a springstrip W clamped to such plate, whilst the lower two'VWsimilarly engagein recesses-in the body of the fixed base W'and in a'spring strip W clamped to the base.

At its rear end the horizontal plate W is connected to the base Wthrough a link'"X and'to thegcontrolled 'bar'W through a link Y, whichalso extends upwardly above the horizontal plate.

The-- nected bythe traversing memberandby'atleast end of ahatchet-shaped distance piece Y having a ballY at its other end'engagingin a recess in a spring strip W clamped to the horizontal plate W At itsupper end thelink Y carries a'block 1 Y having a recess for receivingthe ball-shapedend Y of a link Y h'whose other end is likewise" formedas a ball Y engaging in a recess in a bracket W carried bythe fixed baseW A tension spring Y is provided to hold the link Y in engagement in itsrecesses.

Z..having ratchet teeth coacting with a half-nut Z supported in acradleZ on a vertical postlZ slidable' in a block Z carried by thecontrolled bar W a tensionspringZ connecting the controlled 1 bar with a.pin:Z .on the fixed base W. The fulldetails of this. drivingvmechanism-and of the operatiomof the whole arrangement will beapparentfromthedescription already given in con-- nection'with theconstruction of Figures 2 to '7.

Whatwe claimv as our invention anddesire to; secure by Letters Patentis:

1.. A pickeup :unit foruse in apparatus for measuring or indicating theroughnessesz orundulationsofa surface, comprising .a casing," meanswhereby the casing can'be located inany chosen position relatively totheJ surface under investigation, a stylus for engaging with the surface,aupick-up headcarrying the stylus, a traversing member carrying thepick-up head, link mechanism constituting an interconnection"betweenithe casing and the traversing member andecmprising a group ofmutually pivoted links constituting in efiect two'straight-linelinkagesrespectively constraining two points of the said membento performsubstantially straight-line straight-line path" determined by" the link"mechanism;

2. A'pick-up unit as'claimed in claim 1, in" which the link mechanismcomprises; two in complete straight-line linkages which' are cononeadditionallink spaced apart from the traversing member and from fixedpoints of the linkages, the omitted parts of the two linkages beingthose which are rendered redundant by such interconnections whereby thelink mechanism will operate as though the redundant parts had not beenomitted. l

3. The combination with the features claimed in claim 1,'of meanswhereby the angle between the line joining the two points of thetraversing member constrained by the linkages and the direction ofmovement of such points can be varied.

4'. A pick-up unit as claimed in claim 1, in which the link mechanismcomprises a group of links in effect constituting twostraight-linelinkages each having two pivot points which re-;

main fixed during operational movement, the link mechanism beingotherwise unconstrained within predetermined limits of movement.

5. A pick-up unit as claimed in claim 1, in which the link mechanismcomprises a group of links in effect constituting two straight-linelinkages each having three links of appropriately related lengths, ofwhich the first carries the tracing point of the linkage constituting asupporting point for the traversing member, whilst the other two areeach pivoted to the first link and also to a point which remains fixedduring operational movement.

6. A pick-up unit as claimed in claim 1, in which the link mechanismcomprises a group of links in efiect constituting two straight-linelinkages each having one pivot point which remains fixed duringoperational movement and one other point which is in effect guided tomove along an approximately straight path.

'7. A pick-up unit for use in apparatus for measuring or indicating theroughnesses or undulations of a surface, comprising a casing, meanswhereby the casing can be located in any chosen position relatively tothe surface under investigation. a stylus for engaging with the surface,a pick-up head carrying the stylus, a traversing member carrying thepick-up head, link mechanism within the casing comprising a group ofmutually pivoted links constituting in effect two straight-line linkagesrespectively constraining two points of the said member to perform atleast approximately straight line movements in the same direction, anddriving means cooperating with the link mechanism to cause thetraversing member and the pick up head to be traversed over the surfacealong the straight line path determined by the link mechanism, each ofthe two linkages having two links, of which the first carries at one endthe tracing point constituting a supporting point for the traversingmember carrying the pick-up head and has its other end in effect guidedto move along an approximate straight path, whilst the second has alength equal to half that of the first link and is pivoted at one end tothe midpoint of the first link and at the other end to a fixed pivotapproximately collinear with the path of the guided end of the firstlink.

8. A pick-up unit as claimed in claim 7, in which the interconnectionsbetween the two linkages include, in addition to the controlled member,at least one additional link connecting a pair of corresponding pointsof the two linkages spaced apart from the controlled member and from thefixed pivots of the linkages, and the guided end of at least one of thetwo first links is omitted, the guiding of such first links beingbrought about in effect by pivoting one point of the link mechanism toone end ofa relatively long guiding link pivoted about a center at itsother end.

9. The combination with the features claimed in claim 8, of means foradjusting the position of the center about which the relatively longguiding link is pivoted whereby the angle be-.

tween the line joining the two pivot points of the traversing member andtheir direction of movement can be varied.

10. A. pick-up unit for use in apparatus for measuring or indicating theroughnesses or undulations of a surface, comprising a casing, meanswhereby the casing can be located in any chosen position relatively tothe surface under investigation, a stylus for engaging with the surface,a pick-up head carrying the stylus, a traversing member carrying thepick-up head, link mechanism within the casing comprising a group ofmutually pivoted links constraining two points of the said member toperform substantially straight-line movements in the same direction, anddriving means cooperating with the link mechanism to cause thetraversing member and the pick-up head to be traversed over the surfacealong the straight-line path determined by the link mechanism, the linkmechanism comprising in combination with the traversing member, twopairs of links of equal length, the first link of each pair beingpivoted at one end to the traversing member whilst the second link ofeach pair is pivoted at one end to a fixed point, an additional linkpivoted at one point to the other ends of the first and second links ofone pair and at another point to the other ends of the first and secondlinks of the other pair, the line joining the two pivot points of theadditional link being equal and parallel to that joining the two pivotpoints of the traversing member and also that joining the two fixedpivots, and means for causing movement of the additional link to takeplace at half the speed of that of the traversing member whereby the twopivot points of the traversing member are constrained to move; alongapproximately straight-line paths in the same direction withinpredetermined limits of movement.

11. A pick-up unit as claimed in claim '7, in which the link mechanismcomprises two incomplete linkages each consisting of a pair of linkspivoted together, the first link of each pair also being pivoted at afixed point whilst the second link of each pair is also pivoted to thetraversing member at the tracing point of the linkage, the distances ofthe junction pivots of the two pairs from the two fixed pivots and fromthe two tracing points all being equal to one another, an additionallink connecting a pair of corresponding points of the two linkagesspaced apart from the traversing member and from the fixed pivots of thelinkages, and means for imposing a constraint on the link mechanismequivalent to the constraint which would be imposed thereon by providinga guided end to the second link of either pair at the same distance asthe tracing point from the junction pivot on the other side thereof andguiding such guided end to move along an approximately straight pathapproximately collinear with the fixed pivot of the pair, such meanscomprising a relatively long guiding link pivoted about a center at oneend so that its other end constitutes a guided point movable along anapproximately straight path parallel to the path 15 eithe -said guidedendand a 'paralieleiink com motion between such'guided point and the twopai-rs of linkswh'ereby the movements of the said guided point is ineffect transferred to the said guided end.

12. The combination with the features claimed in claim 11, of means foradjusting the position of th'ecenter about which the relatively longguidinglink is'pivoted, whereby the angle be'-' tween-"the linejoiningthetwo pivot points of the traversing member and their direction ofmovement can be varied.

13.A-pickup unit for use in apparatus for measuring the roughness of asurface; comprising a casing,means' whereby the casing can be loc'atedin any chosenposition relatively to the surfaceunder investigation, astylus for engaging the surface, a pick-up head carrying the'stylus, 'atraversing member carrying the pick-up head, link mechanism constitutingin effect two-straight line' linkages respectively constraining twopoints of Said member to perform substantially straight-line movementsin th'same direction, said mechanism comprising two'pairs of linksthe'two links of each pair be ing pivotally connected together, twocorrespondinglinks' of' the pairs being pivoted to saidmeinber-respectively at said points and the other link of each pairbeing pivotally connected 16'' to the'ca'sing; guiding means"between onepair of links and the" casing r for" eontromng sthe angular relationbetweemthe links of said one pair throughout the entire movement or said1 other link'of said one'pair,- and a linkcbnhedt ing the points'ofinterconnection of the two" links of each pair to maintainc'o'ri'espending links'of' the two'paii's p-ara11e1 with onean'otl'ierl' RICHARD EDMUND REASON: DONALD 'ROY BER RIDGEE i REFERENCESCITED The following references are of record 111* the" file 'of thispatent:

